• Electrical & Electronic Materials
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• v.8 no.4
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• pp.443-450
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• 1995

A directional coupler which on the X-cut $LiNbO_3$ substrate is fabricated by using proton exchange method and self-aligned method. After proton exchange process, the waveguide is formed by annealing process. The relation ship between refractive index change of waveguide and maximum output was studied along with the annealing time. A self-aligned method was used to simplify the fabrication process of the waveguide and to maximize the efficiency of electric field. The on-off state of modulator has been observered with the switching of the directional coupler by the electric field effect and also the switching voltage of the directional coupler has been measured with 8.0 [V].

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.19 no.5
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• pp.175-180
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• 2019

The optical characteristics and power transfers between guiding channels of blazed grating-assisted directional coupler (B-GADC) are evaluated in detail by using novel and rigorous modal transmission-line theory (MTLT) based on eigenvalue problem. To evaluate the coupling efficiency of B-GADC, the dispersion curves as a function of the grating period and wavelength are analyzed numerically for quasi-TE and quasi-TM modes. Furthermore, symmetric, sawtooth and asymmetric grating profiles are considered to know the effect of blazing characteristics on power transfer of GADC. The numerical results show that the grating period for minimum-gap condition to obtain maximum power transfer decreases gradually as the blazed structure changes from symmetric to asymmetric profile. On the other hand, the coupling length increases reversely.

• Current Optics and Photonics
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• v.1 no.1
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• pp.65-72
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• 2017

We propose a nearly lossless, compact, electrically modulated vertical directional coupler, which is based on the controllable evanescent coupling in a previously proposed graphene-assisted total internal reflection (GA-FTIR) scheme. In the proposed device, two single-mode waveguides are separate by graphene-$SiO_2$-graphene layers. By changing the chemical potential of the graphene layers with a gate voltage, the coupling strength between the waveguides, and hence the coupling length of the directional coupler, is controlled. Therefore, for a properly chosen, fixed device length, when an input wave is launched into one of the waveguides, the ratio of their output powers can be controlled electrically. The operation of the proposed device is analyzed, with the dispersion relations calculated using a model of a one-dimensional slab waveguide. The supermodes in the coupled waveguide are calculated using the finite-element method to estimate the coupling length, realistic devices are designed, and their performance was confirmed using the finite-difference time-domain method. The designed $3{\mu}m$ by $1{\mu}m$ device achieves an insertion loss of less than 0.11 dB, and a 24-dB extinction ratio between bar and cross states. The proposed low-loss device could enable integrated modulation of a strong optical signal, without thermal buildup.

• Proceedings of the Optical Society of Korea Conference
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• 2007.07a
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• pp.351-352
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• 2007

• Proceedings of the Optical Society of Korea Conference
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• 2004.02a
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• pp.132-133
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• 2004

• Journal of the Korean Institute of Telematics and Electronics B
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• v.32B no.11
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• pp.1481-1488
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• 1995

Due to the low loss, broadband and accurate short time delay properties of optical fiber, it has attracted as a delay medium for high speed and broad-band signal processing. In this paper, we consider the coherent optical fiber filter of IIR lattice structure, which uses coherent light sources and consists of directional couplers whose coupling coefficients are restricted between 0 and 1. Considering restrictions of directional coupler, the design formulae and condition for realibility of optical fiber filter of IIR lattice structure which makes the optimal use of optical signal energy are derived.

• Proceedings of the Optical Society of Korea Conference
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• 2000.08a
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• pp.24-25
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• 2000

파장변환 소자는 최근에 급격히 발전하는 광네트웍을 구축하기 위하여 필수적인 소자로서 여러 가지 형태에 대한 연구개발이 진행되고 있다. 그중에서도, 최근에는 반도체 광증폭기로 형성된 방향성 결합기구조(semiconductor optical amplifier directional coupler)에서의 상호 이득 포화(XPM : cross-phase modulation)에 의한 파장변환에 대한 개념이 제안되고 가능성이 실험적으로 입증된 바 있다. 이런 구조의 파장변환 소자는 입력 광신호의 파워가 작을때는 위상 정합이 되어 반도체 광증폭기의 광모드가 완전히 결합되어 cross state로 변환된 파장의 광파워가 많이 출력되고, 신호 입력 파워가 증가함에 따라 결합이 감소하게 되어 Cross state에서의 출력 파워는 감소하게 된다. 이와 같은 소자는 입력 신호광과 변환된 신호광이 역방향으로 진행하는 경우 광필터가 필요없이 파장변환이 가능하고, 변환 후의 소광비가 향상되기 때문에 향후 다양한 형태로 응용될 가능성이 있으며, 적정 설계 및 성능 예측을 위해서는 시영역에서 모델링할 수 있는 방법론을 구축하는 것이 필요하다. 본 논문에서는 연산자 분리 방법$^{(1)}$ 을 적용하여 상술한 파장변환기를 해석하기에 적당하도록 시영역 동적 모델을 구현하고, 파장변환 특성을 여러 가지 면에서 분석하여 보았다. (중략)

• Korean Journal of Optics and Photonics
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• v.15 no.6
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• pp.503-510
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• 2004

We propose a novel vertical directional coupler switch using a vertical directional coupler with polarization independent coupling lengths employing the doublesided deep-ridge waveguide structure. This switch is composed of a switching operation induced section with symmetric structures and an extinction ratio enhanced section with asymmetric structures. We present design methods and examples for this switch with very short lengths and very high extinction ratios larger than 30 dB for both TE and TM modes in cases of both cross and bar states.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.7
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• pp.25-31
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• 1998

Modal transmission-line is utilized to analyze the power coupling of optical directional coupler composed by two parallel guiding slabs. By defining a coupling efficiency .eta. amenable to rigorous supermodes and boundary conditions of modal functions, we evaluate the power transfer for TE mode of gainy coupler. The results reveal that optimized power exchange occurs at a novel wavelength .lambda.$_{op}$ , which is generally different from minimum gap .lambda.$_{min}$ between rigorous modes and phase-matching condition .lambda.$_{ph}$ .

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.23 no.5
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• pp.145-150
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• 2023

Non-uniform optical taper waveguides have been widely used as devices for high-efficiency mode coupling, as they are integrated with single-mode optical fibers or photonic crystal waveguides. In this paper, we present a new platform for chemical sensing and bio-sensing using optical taper waveguides with these characteristics. The principle of operation is based on the coupling efficiency and interference properties of optical directional coupler (DC) and multi-mode interference coupler (MMIC). First, the curvature characteristics of taper sections of DC and MMIC is explained, and the design specifications of optimized taper waveguide to increase waveguide sensitivity is selected. Next, the sensor response to the change in refractive index of sensing analyte is numerically analyzed. Numerical results show that as the length of couplers increases, the effective index per change in refractive index unit (RIU) of analyte increases, and that sensitivity can be tuned using taper DC and MMIC design techniques.